Added check for constructor nodes
Added check for constructor nodes

On constructor nodes the following error would trigger;
```
/Users/Jorick/Sites/animo-web-2.0/node_modules/gulp-neuter/node_modules/neuter/lib/scanner.js:213
				if (childNode.type === 'FunctionDeclaration' ||
				             ^
TypeError: Cannot read property 'type' of undefined
    at Immediate._onImmediate (/Users/Jorick/Sites/animo-web-2.0/node_modules/gulp-neuter/node_modules/neuter/lib/scanner.js:213:18)
    at processImmediate [as _immediateCallback] (timers.js:358:17)
```

This commit fixes this problem.
squarewolf/node-neuter